Drawing plug



Oct. 31, 1961 .1. J. PONCAR 3,006,460

DRAWING PLUG Filed April 30, 1959 2 Sheets-Sheet 1 F ig 3 INVENTOR.

JOHN J. PONCAR BY M M ATTORNEYS 1961 J. J. PONCAR 3,006,460

DRAWING PLUG Filed April 30, 1959 2 Sheets-Sheet 2 A \E i 23 5 F/g. 8 I 9 I JOHN J. PONCAR ATTOR NEYS 7 United States Patent 3,006,460 DRAWING PLUG John J. Poncar, 4189 Brainard Road, Cleveland, Ohio, assignor of one-half to Bruce B. Krost Filed Apr. 30, 1959, Ser. No. 810,020 8 Claims. (Cl. 205--7) My invention relates to drawing plugs for the drawing of tubes through a die to a reduced diameter.

An object of my invention is to provide an improved drawing plug constructed for producing superior results in the tube being drawn.

Another object is the provision of a plug so constructed as to avoid injury and scoring of the inner wall of a tube being drawn over the plug.

Another object is the provision of a plug having its parts so arranged as to permit the escape of material scraped from the inner wall of the tube being drawn rearwardly of the plug and without being forced forwardly of the tube between the plug and the inner wall of the tube.

Another object is the provision of a drawing plug having a novel construction which permits accumulated material scraped from the inner wall of the tube to escape inwardly of the plug and thence rearwardly so as to avoid scoring or other defacement of the inner wall of the tube after its reduction in diameter.

Another object is the provision of a drawing plug having a novel construction which produces a tube of reduced diameter and with a clean and uninjured surface on the inner wall of the tube as it is drawn to reduced diameter.

Another object is the provision of an improved plug producing results not heretofore obtainable.

Other objects and a fuller understanding of my invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a longitudinal sectional view of a preferred form of my plug in a tube being drawn through a reducing die;

FIGURE 2 is a cross-sectional view through line 2-2 of FIGURE 1;

FIGURE 3 is a longitudinal sectional view of a modified form of my plug positioned in a tube being drawn through a reducing die;

FIGURE 4 is a form of plug somewhat modified from the form shown in FIGURE 1 and also illustrating a longitudinal sectional view of the modified plug;

FIGURE 5 is a cross-sectional view through the line 5-5 of FIGURE 4;

FIGURE 6 is a longitudinal sectional view of another modified form of my plug shown positioned in a tube being reduced in diameter;

FIGURE 7 is a longitudinal sectional view of another modified form of my plug shown positioned in a tube being reduced in diameter;

FIGURE 8 is a cross-sectional view through the line 8-8 of FIGURE 7; and

FIGURE 9 is a longitudinal sectional view showing another arrangement of the parts in my plug, also shown in a tube being reduced in diameter.

In the drawings, the reducing die is illustrated by the reference character 11, the die is mounted in a stationary position in the drawing apparatus. The die has a cylindrical opening 12 having a diameter complementing the reduced outside diameter of the tube being drawn. The die 11 has a throat 13 which has a sloping wall of gradually diminishing diameter leading from the rearward face of the die 11 to the round or cylindrical opening 12.

A tube 14, such as a copper, aluminum or brass tube,

3,006,460 Patented Oct. 31, 1961 whose inner and outer diameter is to be reduced, is drawn toward the right in the drawings as indicated by the arrows at the right-hand end of the tube 14. Apparatus somewhat similar to that illustrated in US. Patent No. 2,196,646 and US. Patent No. 2,306,712, may be utilized for drawing or pulling the tube 14 through the die 11 so as to forcibly reduce its diameter in the wellknown drawing operation.

To provide for the reduction of the tube so as to have the required inner diameter and to prevent its collapse or distortion while being drawn through the die, a drawing plug is positioned in the tube and within the die as illustrated. My drawing plug has a forward cylindricallyshaped bearing portion 16 which is located within the round or cylindrical opening 12 of the die and which supports and sizes the inner wall of the tube 14 at the location of reduced diameter. A rearward bearing portion 17 of my drawing plug is positioned rearwardly of the forward portion 16 and it has an outer diameter greater than the outer diameter of the forward portion 16. As seen in the drawing, the rearward bearing portion 17 is greater in diameter than the cylindrical opening 12 and cannot pass through the opening 12 even if the plug is free to float within the die.

Located rearwardly of the rearward bearing portion 17 is an adaptor 18, to which the forward portion 16 and the rearward portion 17 are carried by a threaded bolt 20. The adaptor 18 thread'ably engages the forward end of a rod 19 which has its rearward end supported and carried limits by the rearward end of the apparatus, such as shown, for example, in said US. Patent No. 2,306,712. Thus, the plug floats to some extent the tube at the position illustrated but the .plug may be withdrawn from the tube by means of the rod 19 carrying the plug. The threaded end 20-a of the bolt 20 is threadably engaged in the said end of the adaptor 18 and is secured in locked position by opposed set screws 24. The length of the bolt 20 and its threaded engagement in the adaptor 18 is such that there is left a crevice or crack 28 between the forward portion 16 and the rearward portion 17. By reason of the frictional engage-v ment of the forward portion 16 on the inner wall of the tube 14 as the tube is drawn forwardly, the forward portion '16 tends to move forward in the tube 14 against the head of the bolt 20, while the enlarged rearward portion 17 is held back by reason of its greater diameter relative to the opening 12 and this maintains the crevice or crack 28 between the parts 16 and 17.

It is to be noted that the rearward portion 17 is curved or reduced as it extends forwardly and radially inward, as illustrated in the drawing. There is an annular bearing surface 25 which firmly engages and firictionally scrapes the inner wall of the tube 14 as it is being gradually reduced in diameter through the throat 13 of the die. There is also an annular bearing surface 26 extending around the forward portion 16 and extending along the major portion of its length. The bearing surfaces 25 and 26 may be considered as rings of contact between the tube 14 and the portions 16 and 17, respectively. 0onsiderable pressure is applied upon these bearing surfaces by the tube as it is forcibly drawn across these bearing surfaces. By reason of the lesser diameter at the bearing surface 26, the pressure upon the bearing surface 26 imposed by the tube 14 within the constriction of the round opening 12 is considerably greater than that imposed by the bearing surface 25 on the inner wall of the 11 e.

In commercial practice, most tubes being drawn have the interior wall coated with various substances; for example, the wall is purposely coated with lubricating soap so as to help reduce the frictional drag on the tube as it is drawn. Also the interior wall of the tube tends to accumulate dirt and other foreign material. Also the interior wall of the tube tends to collect slivers or detached or partially detached particles of metal of the tube which adhere to the inner wall of the tube. All

. of such materials tend to be scraped from the inner Wall of the tube by the bearing surface 26 as the tube is drawn through the die.

By reason of the radial curvature of the rearward portion 17 and the cylindrical shape of the forward portion 16, there is provided an annular recess 27 extending around the plug and between the bearing surface 25 and the bearing surface 26. This recess 27 normally tends to be pressed solidly with this material scraped from the inner wall of the tube. The material has considerable pressure applied thereto by reason of the rearward bearing surface 25 of the part 17 preventing therearWard escape of the material as the tube is drawn forwardly. The pressure on the accumulated material may be sufficient to force the material to leak forwardly along the inner wall of the tube between the forward portion 16 and the inner wall. Upon the material so leaking forwardly, it tends to deface and score the inner wall of the tube and particularly if the material contains slivers or loose particles of metal. Even without such slivers or particles of metal, such material upon leaking forwardly of the plug is so pressed against the inner wall of the tube as to dirty the inner wall and to dispose a hard and undesirable crust of dirt and soap upon the inner wall of the tube.

1 provide means for permitting the escape of the accumulated material pressed into the annular recess 27. This escape means includes the crevice or crack 28 which permitsthe material under pressure to work or flow radially inward between the portions 16 and'17. As seen particularly in FIGURES l and 2, I provide on the inner bore of the rearward portion 17 through which the shank of the bolt 20 extends two longitudinally extending grooves21 which parallel and extend along the shank of the bolt. These grooves 21 permit the accumulated material pressed down in the crack or crevice 28 to move rearwardly. through the plug.

' On the forwardfaceof the adaptor 18 where it adjoins the rearward portion 17, I provide a round recess 22 into which the material working rearwardly through the grooves 21 may enter. There are two transverse grooves 23 extending outwardly of the adaptor 18 on its for-ward face from the round recess 22 to the outer circumferential surface of the adaptor 18. Material thus pressed 4 to work inwardly to the shank of the bolt past the spacer 29.

To provide a longitudinal passageway through the plug, I provide an enlarged bore 21-a for the rearward portion 17 in the place of the two opposed transverse grooves 23 of the arrangement shown in FIGURES 1 and 2. Although the enlarged bore 21a' of the rearward portion 17 is considerably greater than the outer diameter of the bolt 20, the rearward portion 17 nevertheless is maintained substantially concentric with the axis of the bolt by the aligning action imposed on the rearward portion 17 during the drawing operation. 7

The passageway provided by the enlarged bore 21-a empties rearwardly into the round recess 22 provided on the forward face of the adaptor 18. Again, as in the case of the arrangement of 'FIGURES 1 and 2, the material pressed into the round recess 22 from the enlarged bore 21-11 moves outwardly through the two transverse grooves 23. Thus, the material scraped from the wall of the tube into the annular recess 27 is by-passed through the plug rearwardly past the bearing surface 25 by the escape means of'the modified arrangement shown in FIGURES 4 and 5.

In the modified arrangement of FIGURE 3, the drawingplug is ofone integral piece of steel or other suitable metal, whereas the drawing plug in FIGURES 1 and 2 and FIGURES 4 and 5 was assembled of portions 16 and 17 held to a rod adaptor 18 by a bolt 20. The drawing plug shown in FIGURE 3 has a fonavardbearing portion 31 and a rearward bearing portion 32 of the same integral piece. The rearward bearing portion 32 has a radial curve as it extends forwardly and inwardly toward the forward bearing portion 31. This con-tour leaves the annular recess 33 into which the material scraped by the plug during the drawing operation is pressed. The annular recess 33 extends longitudinally of the tube between the rearward annular bearing surface 35 and the forward annular bearing surface 34.

' The escape means to permit the material pressed into the rearwardly into the round recess 22 from the grooves 21 may escape radially outwardly into the large part of the tube 14 at a location rearwardly of the annular bearing surface 25. Although the material takes a circuitous path through the crevice, longitudinal grooves, recess and transverse grooves, the material is under such pressure that it may flow through this path and thus escape rearwardly into the tube at a location where it is free of pressure imposed by the plug. The arrangement permits 7 r a circulation of the soap or other lubricant so as to permit the proper lubrication of the tube being drawn over the plug and at the same time prevents such a build-up of pressure in the annular recess 27 as to stop or minimize the possibility of such material being squeezed forwardly past the forward bearing portion 16, that is between the forward bearing surface 26 and the inner wall of the tube.

The plug as illustrated in FIGURES 4 and 5 is slightly modified from the arrangement illustrated in FIGURES ,1 and 2. In the arrangement of FIGURES 4 and 5, I provide a spacer element 29 in the crevice or crack 28 for the maintenance of a constant spacing between the portions 16 and 17. Upon the bolt 20 being turned down tight, the portions 16 and 17 clamp the'spacer 29 in position and fix the dimension of the crack 28. The spacer 29 is such that it does not extend completely around the shank :of the bolt and permits the material annular recess 33 to leave is provided by a plurality of diagonally drilled holes or ducts 36 extending both longitudinally and transversely of the rearward portion 32. In the form illustrated, there are four diagonally disposed holes or ducts 36. Each hole or duct 36 extends from the bottom of the annular recess 33 rearwardly and transversely to the opposite outer wall of the rearward portion 32 of the plug so as to permit material to flow from the recess 33 through the hole or duct 36 rearwardly of the bearing surface 35 to within the tube. As there are four holes or ducts 36, these are arranged equidistantly around the plug so that material pressed into the annular recess 33 may flow rearwardly of the plug through the most adjacent hole or duct 36. By reason of the spacing between the inner wall of the tube 14 and the outercylindrical wall of the rearward portion 32, the material discharged from the holes or ducts 36 is free and uncompressed. I 7 i In the form of plug illustrated in FIGURE 6 a simple escape arrangement for the scraped material is provided by two or more grooves or slots 43 formed in the rearward portion 39 of the plug there illustrated. In that plug shown in FIGURE 6, an annular recess 40 is provided between the rearward annular bearing surface 42 and the forward annular bearing surface 41. The grooves or slots 43 cut into the outer wall of the rearward portion 39 at spaced locations around the circumferential extent of the plug permit the maten'alpressed 'into the annular recess 40 to escape rearwardly through the rearward portion 45 by a threaded bolt 46, the rearward portion 45 having a radial curvature as it extends forwardly and rearwardly toward the forward portion 44 as illustrated in the drawings. 'In this form of FIG- URE 7, the material pressed into the annular recess 48 by the annular bearing surfaces of the respective forward and rearward portions escapes radially inward from the recess 48 through two transversely extending grooves 49. These grooves 49 extend from the bottom of the annular recess 48 to the shank of the bolt 46. The threaded shank of the bolt (threadably interengaged with the rearward portion 45) has on opposite sides thereof two flats 47 formed thereon, these flats 47 in effect providing grooves along the shank of the bolt and extending to the end of the bolt 46. At the forward face of the rearward portion 45 and extending around the shank of the bolt 46 radially inward of the grooves 49 is a round recess 50. Material pressed radially inward of the grooves 49 from the annular recess 48 enters the round recess 50 and thence moves rearwardly along the passageway provided by the flats 47 to the end of the bolt 46.

Centrally of the rearward portion 45 and in alignment with the bolt 46 is a central opening 51. Extending radially outward from this central opening 51 to the opposite sides of the rearward portion 45 are two transverse holes 52. Thus, material pressed rearwardly into the central opening 51 from the passageways provided by the flats 47 may move radially outward through the transverse holes 52 to the interior of the tube and within the open space between the inner wall of the tube and the rearward portion 45 at a location rearwardly of the annular bearing surface of the rearward portion 45. Set screws 53 secure the bolt 46 in fixed position to the rearward portion 45.

In FIGURE 9 the plug also has a cylindrical forward portion 55 bolted to a rearward portion 56 by a threaded bolt 59. The setting of the bolt 59 is such as to leave a crack or crevice 58 between the portions 55 and 56. An annular recess 57 between the rearward annular bearing surface and the forward annular bearing surface of the plug accommodates material scraped from the inner wall of the tube 14 as it is drawn through a die, such as die 11, over the plug. This material pressed into the annular recess 57 moves radially inward through the crack or crevice 58 between the portions 55 and 56. In the arrangement for escape of this material illustrated in FIG- URE 9, I provide a longitudinally extending opening 60, which extends the length of the rearward portion 56 from the crack or crevice 58 to the rear face of the rearward portion 56. There is also shown another escape means for this material, this being the angularly disposed opening 61. The opening 61 extends initially from the crack or crevice 58 rearwardly therefrom and thence radially outward to the exterior of the plug to the space between the rearward portion 56 and the inner wall of the tube at a location rearwardly of the rearward annular bearing surface of the rearward portion 56. As the space within the tube rearwardly of the rearward annular bearing surface defining the rearward limit of the recess 57 is free of the pressure imposed on the material by the scraping action of the rearward annular bearing surface of the plug, the material scraped from the inner wall may readily flow under pressure from the recess 57 and thence escape rearwardly into the tube.

It has been found in practice, that by the novel structure here disclosed, tubes of superior quality are drawn which are free from defects on the inner surface thereof which otherwise are created by the material scraped from the tube being pressed forwardly between the forward bearing surface of the plug and the inner wall of the tube at its location of reduced diameter. The cost and difficulty of afterwards cleaning the tubes of soap or other lubricant and the dirt and foreign material mixing therewith is obviated by the use of this invention. Clean tubes free from scratches and scoring on the inner walls thereof are produced in the same operation as the drawing of the tube to reduce diameter. Other advantages and benefits are readily apparent to those having knowledge and experience in this field of drawing tubes with the use of drawing plugs.

The present disclosure includes that contained in the appended claims, as well as that of the foregoing description.

Although this invention has been described in its preferred form with a certain degree of particularity, it is understood that the present disclosure of the preferred form has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

What is claimed is:

1. An improved drawing plug for use inside of a tube being drawn through a tube-drawing die having a gradually diminishing bore into which the tube is advanced and a cylindrical bore coinciding with the minimum diameter of said gradually diminishing bore and through which the tube is drawn from the gradually diminishing bore to reduce its outside diameter to the diameter of said cylindrical bore, said drawing plug having a bearing portion adjacent its forward end, said bearing portion having a substantially cylindrical outer wall adapted to be located within said cylindrical bore and to bean'ngly engage the inner wall of said tube being drawn radially inwardly of said cylindrical bore, said drawing plug having an enlarged drawing portion, said enlarged drawing portion having a diameter larger than the diameter of said hearing portion and larger than the diameter of said cylindrical bore, said drawing portion having an annular surface adapted to bearingly engage the inner wall of said tube radially inwardly of said gradually diminishing bore, said bearing portion scraping the inner wall of said tube as the tube is drawn to smaller diameter through the cylindrical bore of said die and pushing material scraped from said inner wall rearwardly toward said annular surface of the drawing plug, said drawing portion extending forwardly of said annular surface toward said bearing portion in a gradually diminishing diameter decreasing at a rate in excess of the rate of decrease of the said gradually diminishing bore to allow an annular open space within said tube extending longitudinally of said tube between said annular surface and said bearing portion, said annular open space being adapted to accommodate said scraped material, the drawing plug at said annular surface obstructing the rearward movement of said scraped materialbetween the inner wall of the tube and said annular surface to subject said scraped material in said open space to pressure from the accumulations of scraped metal during the drawing operation, said drawing plug having an opening extending therethrough from said annular open space at a location radially inward of the maximum circumference of said annular surface to a location rearwardly of said annular surface to permit said scraped material under said pressure to escape from said annular open space rearwardly of said annular surface.

'2. A drawing plug for drawing a tube through a die to reduce the diameter thereof, said die having a cylindrical bore of minimum diameter and a throat having sloping walls extending forwardly to said bore, said plug having a forward portion positionable in said cylindrical bore of the die and having a diameter to coincide with the inside diameter of the tube at a location of the reduction of the tube in said die to its minimum drawn diameter, said forward portion providing first annular bearing surface closely engaging the inside wall of the tube at the location of its minimum diameter as it is drawn through the die past said plug, said plug having a rearward portion having a maximum diameter greater than the diameter of said forward portion, said rearward portion having second annular bearing surface positioned rearwardly of said forward portion and adapted to bearingly '7 engage the inner wall of said tube at a location spaced rearwardly of the said location of minimum diameter,

7 the said first annular bearing surface scraping said inner wall of the tube as the tube is drawn over the plug through the said throat in said die and pressing rearwardly any material thereby scraped from said inner 'wall, the. outer wall of said plug extending forwardly.

drawing operation tending to subject the scraped mate-,

rial in said annular groove to pressure, said plug having a passageway provided between said first and second annular bearing surfaces opening into said annular groove and extending radially inward and longitudinally of the plug and opening outwardly of the plug at a location rearwardly of the second annular bearing surface to permit scraped material lodged in said annular groove and subjected to said pressure to escape rearwardly of said second annular bearing surface through said passageway without being forced forwardly between said forward portiontof the plug and the inner wall of the tube at its location of minimum drawn diameter.

3. In drawing apparatus adapted to have a metallic tubedrawn over a drawing plug through a'die for reducing the inner and outer diameters of the tube, the die having a round opening adapted to limit the outer diameter of the tube being drawn and a funnel-shaped throat leading to the round opening, the throat having inclined walls extending toward the round opening for cammingly gradually reducing the outside diameter of the tube being drawn, the improvement of a drawing plug having a cylindrical forward portion adapted to bearingly support the inner wall of the tube within said round opening to limitrthe reduction of the inner diameter of the tube, said drawing plug'having a rearward portion, said rearward portion having an annular bearing surface adapted to engage the inner wall of the tube in said throat and being of a diameter greater than the dianiete'rf of said forward portion, said rearward portion extending forwardly and inwardly from said annular bearing surface in a radial curve toward said cylindrical forward portion to provide an annular relief forwardly of said annular bearing surface, said annular relief accommodatingmaterial scraped from the inner wall of the tube by said drawing plug as the tube is drawn through the said round opening of the die over said cylindrical forward portionQthe accumulation of scraped material during the drawing operation exerting pressure on the sf cra ped material accommodated in said annular relief, said plug having an open space extending radially inward of the plug proximate to the junction of said cylindrical forward portion and said rearward portion to ccmmunieate with said annular relief, said plug having an opening extending longitudinally of said rear portion from said open space and terminating outwardly of the said plug at a location rearwardly of said annular'bearing surface to permit said material under pressure and accommodated'in said annular relief to escape therefrom rearwardly of said annular bearing surface as the tube is drawn over the plug.

4.9111 3. drawing plug for the drawing of a tube from an initial diameter to a reduced diameter through a die haw'ng a round opening of said reduced diameter and a throat of gradually decreasing diameter leading to the round opening, said plug having a forward bearing portion-adapted to bearingly engage the inner wall of the distance rearwardly of said forward bearing portion, a reference;frusto-conical plane generated about the axis of said plug through said forward bearing portion and said rearward bearing portion substantially defining the path of the tube 'as'it is" drawn over the plug and extending between said bearing portions, said plug being relieved radially inward of said reference frusto-conical plane and intermediate of said bearing portions to provide an annular recess, material scraped from the inner wall of the tube being drawn being pressed within said annular reces s by the accumulation of said scraped material during the drawing operation and restrained against escape therefrom by said bearing portions, said plug being provided with escape vent means extending longitudinally of the plug from said annular recess through the rearward bearing portion and opening exteriorly of the plug at a location rearwardly of said rearward bearing portion to permit the material pressed in said annular recess to escape rearwardly therefrom.

5. In a drawing plug having a forward annular bearing surface against which the inner wall of a tube being drawn is pressed as the tube is drawn through a round hole in a die and having arearward annular bearing surface against which the inner wall of said tube is pressed as the tube is drawn through a throat of gradually diminishing diameter leading to saidround hole, said bearing surfaces being spaced longitudinally of said plug and said rearward bearing surface being of greater diameter than said forward bearing surface, a plane generated about the axis of said plug and coinciding with said annular bearing surfaces defining a frusto-conical reference plane, movement of said tube being drawn generally following the path of said reference plane in the drawing of the tube over the plug through a said die, the said plug being relieved radially inward of said reference plane to define an annular recess around said plug to accommodate within said tube and intermediate of said forward and rearward bearing surfaces material scraped from the inner wall of the tube and pressed into the recess by the said forward bearing surface engaging the inner wall of the tube as the tube is drawnover the plug through a said die, the improvement of escape means for permitting material pressed into said annular recess to escape therefrom without being forced forwardly between said forward bearing surface and the inner wall of the tube, said esape means including a crevice in said plug extending radially inward of the plug from the bottom of said annular recess and a vent from said crevice extending longitudinally of the plug rearwardly of said crevice and opening outwardly of the plug at a location rearwardly of said rearward bearing surface to permit located at the junction of the said parts and the said crevice being provided by spacing between said parts.

7. The improvement in a drawing plug as defined in claim 6 and in which the rearwardof said separable parts carrying the said rearward annular bearing surface extends in a radialcurve forwardly and inwardly toward the other-separate part carrying the forward annular bearing surface to define a wall of said annular recess forwardly of the rearward annular bearing surface, and

in which the escape means includes a passageway along said bolt in the said rearward of the separable parts from said crevice to the outer wall of the plug'at a longitudinal distance rearwardly of the rearward annular bearing .surface. =8. In a drawing plug having a forward annular bearin 'surface against which the inner wall of a tube being drawn is pressed as the tube is drawn through a round hole in a die and having a rearward annular bearing surface against which the inner wall of said tube is pressed as the tube is drawn through a throat of gradually diminishing diameter leading to said round hole, said bearing surfaces being spaced longitudinally of said plug and said rearward bearing surface being of greater diameter than said forward bearing surface, a plane generated about the axis of said plug and coinciding with said annular bearing surfaces defining a frusto-conical reference plane, movement of said tube being drawn generally following the path of said reference plane in the drawing of the tube over the plug through a said die, the said plug being relieved radially inward of said reference plane to define an annular recess around said plug to accommodate within said tube and intermediate of said forward and rearward bearing surfaces material scraped from the inner wall of the tube and pressed into the recess by the said forward bearing surface engaging the inner wall of the tube as the tube is drawn over the plug through a said die, the improvement of escape means for permitting material pressed into said annular recess to escape therefrom without being forced forwardly between said forward bearing surface and the inner wall of the tube, said escape means including a transverse opening extending radially inward from the bottom of said recess, a longitudinally disposed opening extending rearwardly from said transverse opening parallel to the axis of the plug, and another transverse opening extending radially outward from said longitudinally extending opening to the exterior of the plug at a location rearwardly of said rearward bearing surface.

References Cited in the file of this patent UNITED STATES PATENTS 142,622 Flagler Sept. 9, 1873 307,993 Sharp Nov. 11, 1884 2,355,734 Katz Aug. 15, 1944 2,359,339 Wadell Oct. 3, 1944 FOREIGN PATENTS 8,795 Great Britain Sept. 23, 1915 

